In order to elucidate the mechanisms underlying the nerve impulse it is proposed to study the asymmetry of the change in birefringence displayed by the nerve membrane when subjected to symmetrical voltage pulses, one hyperpolarizing and one depolarizing. This asymmetry will be compared with known asymmetry in the capacity transients seen in response to these pulses (the "gating" current) to look for a direct optical measure of a structural change in the nerve membrane which ultimately leads to the nerve impulse.